1. Field of the Invention
The invention relates to a fuel supply apparatus for an internal combustion engine.
2. Description of Related Art
As illustrated in Japanese Patent Application Publication No. 2002-61529 (JP 2002-61529 A), a fuel supply apparatus for an internal combustion engine that is mounted on a vehicle such as a car is provided with a fuel pump that is driven to rotate so as to discharge a fuel to a fuel pipe which is connected to the internal combustion engine and a pressure regulator that allows the fuel in the pipe to appropriately flow out to the outside based on the fuel pressure in the fuel pipe.
Regarding the fuel supply apparatus, it is conceivable to drive the pump to rotate steadily and at a relatively high rotation speed so that the discharge flow rate of the fuel from the fuel pump sufficiently satisfies a required flow rate of the fuel supplied to the internal combustion engine. This is for the purpose of stably supplying the fuel to the internal combustion engine and simplifying fuel pump driving control. In this case, the surplus fuel in the fuel pipe that is not supplied to the internal combustion engine flows out of the fuel pipe through an operation of the pressure regulator.
When the fuel pump and a component in the vicinity of the fuel pump resonate while the fuel pump is driven to rotate, a resonant sound that is generated by the resonance may make a passenger in the vehicle feel uncomfortable. Accordingly, the rigidity of the component is set so that the natural frequency of the component has a distant value on a lower side with respect to the frequency of the fuel pump that is driven to rotate steadily and at a relatively high rotation speed as described above. Then, the frequency of the fuel pump that is available when the fuel pump is driven to rotate enters a resonance area including the natural frequency of the component, which leads to the suppression of the resonance of the fuel pump and the component in the vicinity of the fuel pump.
The natural frequency (resonance area) of the component is set in an area on the side lower than the frequency of the fuel pump that is available when the fuel pump is driven to rotate because the rigidity of the component needs to be increased and then the cost of the component increases when the resonance area is set in an area on a side higher than the frequency.